BLF / Ringgroups / Other possibilities?

My second question regarding BLF on Grandstream GXP2000 phones.

Again, software used:
BLF / Asterisk 1.6.2 / FreePBX 2.7 / Grandstream GXP 2000

Short explanation, we have 2 stationary reception desks and one mobile reception phone. Therefore I have a ringgroup which calls these 3 phones on an incoming call.

For my other GXP2000 phones, is it possible to put a RingGroup on a BLF Field? I am not so sure if it will work (well, I tried and out of the box it did not) because as I understand SIP Messages are a key part of the BLF implementation and a Ring group is naturaly only a defined extension, not a real SIP Phone per se.

So, what can I do if I want one Button to blink if the phones of my ring group are ringing? Of course this button should be able to answer (pickup) the call and this should behave as if one of the phones from the ring group picked up the call (stop ringing on the other phones).

The other problem is, if I press this button, to call the reception, I want that all the phones in the ring-group ring so everyone in the reception could answer the call.

So how to do it? I was thinking something in the line of putting another (fake) phone into the ring group and use this to pickup and to send the calls to the 3 other phones, but how would I do that without a physical phone?

Is there a better solution to this problem? If I did not explain my problem clearly please tell me what part to write again, english is not my native language.

Thanks for your help,
best regards